Regensburg, Univ., Diss., 2008

Les premières photographies couleurs produites par Edmond Becquerel au Muséum d’Histoire naturelle à Paris en 1848 ont suscité un débat scientifique intense tout au long du XIXème siècle. La question de l’origine des couleurs de ces photographies a vu s’affronter les partisans d’une hypothèse pigmentaire et ceux d’une hypothèse interférentielle. Au cours du XXème siècle, cette question n’a pas été définitivement tranchée. Ce travail doctoral se propose d’appréhender la nature de ces images dites « photochromatiques » par une approche expérimentale. Nous nous sommes dans un premier temps intéressés aux étapes de sensibilisation du plaqué argent et d’exposition de la surface sensible aux rayonnements visibles, dans le but de répliquer le procédé Becquerel et de comprendre la photosensibilité de ces images. Les propriétés optiques des couches sensibles et colorées ont été caractérisées en spectroscopie UV-visible et mises en relation avec leurs compositions chimiques (étudiées en XAS) et leurs morphologies, de l’échelle micro- à nanométrique (étudiées en MEB et TEM). La grande sensibilité des échantillons aux faisceaux photoniques (UV-visible et rayons X) et électroniques a imposé un développement méthodologique afin de comprendre et de limiter les effets de sonde. Les résultats de cette recherche permettent de réfuter l’hypothèse de phénomènes interférentiels comme origine des couleurs des images photochromatiques, hypothèse qui prévaut dans la littérature depuis la fin du XIXème siècle. Les couches sensibles et colorées sont constituées de grains de chlorure d’argent micrométriques décorés de nanoparticules d’argent. Ces nanoparticules d’argent, que nous avons étudiées en EELS low loss, sont responsables de l’absorption dans le visible des couches sensibles et colorées par résonance de plasmons de surface. Ceci nous conduit à proposer une origine plasmonique aux couleurs des images photochromatiques, hypothèse discutée dans cette thèse. / The first colour photographs were produced in 1848 by Edmond Becquerel at the Museum of natural History in Paris. The origin of their colours motivated an intense debate between the scientists during the XIXth century. Two main hypotheses were proposed, namely a pigmentary hypothesis and an interferential hypothesis. Nowadays the question of the colours of those photochromatic images is still not settled and this doctoral research aims at addressing it by an experimental approach. We first studied the sensitizing of the silver plate and the exposure of the sensitive surface to light in order to replicate the Becquerel process and to gain information on the photosensitivity of these images. The optical properties of the sensitized and coloured layers were characterized by UV-visible spectroscopy and related to their chemical composition (studied by XAS) and their morphologies, from the micro to the nanoscale (studied by SEM and TEM). A methodological development was necessary to understand and overcome the sensitivity of the samples to photonic beams (UV-visible and X-rays) and electronic beams. The results allow us to reject the interferential hypothesis, which prevailed since the end of the XIXth century. The sensitized and coloured layers consist in micrometric silver chloride grains decorated by silver nanoparticles. Besides, these nanoparticles, which we investigated by low loss EELS, are responsible for the visible absorption of sensitized and coloured layers through surface plasmon resonance. We suggest that the photochromatic images colours have a plasmonic origin and hereby discuss this hypothesis.

A building with high levels of radon gas in the indoor air has a negative effect on the users of the building. Radon in buildings is one of the most common cause to lung cancer in Sweden today, which is why the Boverkets byggregler have set a limit value of 200 Bq/m3 for indoor air in new buildings. The limit value is twice as high as the limit value set by WHO, due to the high uranium levels in Sweden. The soil conditions in Sweden vary, which leads to the problem with the concentration of radon in the soil being different in different geographical locations in Sweden. The thesis has examined routines regarding radon in the soil at the design stage at Skanska in Helsingborg to highlight the risks of the municipality designating the area as a low-risk area. The methods used in this thesis consists of a survey, interviews and examination of documents and geodata. The survey and interviews were conducted with employees at Skanska in both Helsingborg and Uppsala, in order to make a comparison between two areas where the radon problem differ. The results show that there are gaps in knowledge about radon among the employees in Helsingborg, due to lack of experience. If the municipality does not set requirements regarding radon in the inspection plan, Skanska will not do so either. The results also show from measurements that there are areas in Helsingborg that should be considered a high-risk area for radon. One conclusion for the thesis is that regular internal education regarding radon can be beneficial in an area that is considered a low-risk area, as there is a lack of practical experience. Another conclusion is that it is misleading to generalize an area as a low-risk area, as measured values from radon examination in soils show local differences. A recommendation is therefore to always perform a radon examination before a new building is constructed.